What action should be taken once cleared for an approach?

Once cleared for an approach, the correct action is to maintain the last assigned altitude and heading until established on a segment of the approach. This is essential because it ensures that the aircraft remains within the safely defined airspace while transitioning to the approach procedure, promoting safety and stability.

Maintaining the last assigned altitude allows proper spacing between aircraft, helps prevent altitude intrusions, and keeps the aircraft in a known trajectory until the pilot is ready to follow the approach. It also ensures compliance with air traffic control (ATC) instructions, which are crucial during busy terminal operations where coordination is key.

The other options suggest actions that could compromise safety or violate ATC procedures. For instance, descending immediately to the minimum descent altitude (MDA) could lead to terrain conflicts or unnecessary risks if the aircraft is not yet properly aligned with the approach. Proceeding to the terminal area without altitude restrictions could result in altitude deviations and loss of effective communication with ATC, which could be dangerous in congested airspace. Requesting further vectors could create unnecessary delays and complicate the sequence of arrivals, which may not be appropriate at that stage of the approach. Thus, maintaining the last assigned altitude and heading is the most prudent course of action once cleared for an approach.